The present invention is related to colored and white LED lamps. A purpose of the present invention is to provide a single-chip LED lamp that is up to 250 times more powerful than a conventional single-chip LED lamp. Another purpose of the invention is to provide a two-chip white LED lamp that is up to 250 times more powerful than a conventional single-chip white LED lamp.
Existing single-chip LED lamps are generally of low input power, typically 40-150 milliwatts.
Designers of lamps for outdoor use have had the choice mainly of incandescent tungsten light sources, gas discharge light sources, and LED light sources. Designers of LED-based lamps requiring high power have had to resort to using clusters of single chip LED lamps, each of about 0.1 watt rating, wired in series or in parallel and housed together as a single lamp unit to achieve enhanced power. Providing a lamp unit by clustering single-chip LED lamps is very costly, since it involves making several single-chip lamps, housing them in a unit, wiring them up, and testing the final unit. U.S. Pat. Nos. 5,382,811 and 5,632,551 provide examples of cluster lamps.
Applications for high power LED colored lamps include outdoor displays, which usually have to operate in direct sunlight and so require powerful lamps, and vehicle lights and traffic lights. At present long-life LED traffic lights for use at street intersections need more than a hundred conventional single-chip LED lamps for each lamp unit. The need to use many LED lamps to provide a single LED traffic light is a disadvantage, particularly since only one tungsten light source is needed for a conventional traffic light.
Current blue-green LED traffic lights rely on gallium nitride (GaN) LED technology; whereas amber and red traffic lights rely on aluminum gallium indium phosphide (AlGaInP) technology. It is an object of this invention to provide high power single chip LED lamps in both of these technologies.
Applications for high power LED white lamps include vehicle headlights and reverse lights, vehicle internal lights, torches and other battery powered lighting devices. White single chip LED lamps are available, but they are typically of only about 0.1 watt, unless they are cluster lamps. Furthermore, they rely on a GaN chip that generates ultraviolet or blue light. All or most of this generated light energy has to be converted, using fluorescent material, into longer wavelength components to produce the white light. The light conversion results in loss of light energy. FIG. 31 illustrates the typical spectral distribution of the white light produced. This is quite different from the spectral distribution of daylight, which is represented by dotted line 437.
Prior art single-chip LED lamps having clear convergent lenses, used widely in outdoor displays, suffer not only from the fact that they are of low power but also from the fact that they project light that is not uniform. The non-uniformity is partly due to the bonding pad or pads on the chip top face, which are projected by the lamp as dark areas. The typical width of the bonding pad is about 30-40% of the width of the chip and this is large enough to interfere with achieving good uniformity of projected light even if the LED lens is defocussed relative to top face of the chip. For good quality image displays it is desirable to match the apparent brightnesses of the viewed lamps to within 5%. To achieve this it is important to reduce the non-uniformity caused by the bonding pads.